Police powers to criminalise small, peaceful yet intimidatory protests outside the homes of company directors and others were unveiled yesterday by the home secretary, Jack Straw, in a clampdown targeted at animal rights activists.

He also announced he would increase the penalty for sending hate mail to six months in prison, and would clarify the law so that the act covering malicious communications clearly included email and text messages.

He stopped short of meeting demands from the scientific community that company directors and shareholders should be able to withhold their names and addresses from the companies register. Instead guidance is to be issued on keeping home addresses confidential while still registering them.

The package, tabled yesterday as amendments to the criminal justice and police bill going through parliament, is addressed at the tactics used by animal rights activists trying to close down Huntingdon Life Sciences.

Liberty, the civil rights organisation, said that the proposals would affect many more than animal rights activists. "To make the right to peaceful protest a criminal offence is unnecessary, particularly as the police already have ample powers to arrest people who engage in intimidating acts," said Liberty's associate director, Mary Cunneen.

"We may well sympathise with an individual employee who has a protest outside his house. But will this law end up protecting the official residences of the rich and powerful - cabinet ministers, foreign embassies, and the like?"

Mr Straw said the government could not tolerate the criminal actions of a few extremists who used violence and intimidation to prevent people going about their legitimate business.

"We are determined to make sure that the public are protected and that lawful businesses can operate freely; and, above all, that the appalling harassment - and much worse - of the staff, directors and suppliers of these firms, and their families including children, is dealt with. Peaceful public protest is entirely legitimate, but there is a world of difference between that and the type of intimidation, threats and violence we have seen recently."

The legislation gives the police a new power to move protesters away from homes under the threat of three months in prison or a £2,500 fine if they are likely to "cause harassment, alarm and distress to the residents".

At present the law allows police to deal with assemblies of 20 or more only, and the Home Office believes that public order powers do not cover relatively peaceful protests outside homes.

Roger Lyons, general secretary of MSF, the union representing animal laboratory staff, said the measures would "protect thousands of our members, who undertake vital scientific work, from unjustifiable acts of violence and intimidation".

Natasha Taylor, of the Stop Huntingdon Animal Cruelty campaign, said the measures would not stop the campaign from closing the animal laboratories. "We are running a legal campaign which does not condone illegal activity, but history shows there are always people in the animal rights movement who are prepared to step outside the law in order to achieve an end to animal abuse."